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Path: utzoo!henry
From: henry@utzoo.UUCP (Henry Spencer)
Newsgroups: comp.lang.c
Subject: Re: Optimizing Floating-Point Expression Evaluation
Message-ID: <7919@utzoo.UUCP>
Date: Thu, 16-Apr-87 11:52:52 EST
Article-I.D.: utzoo.7919
Posted: Thu Apr 16 11:52:52 1987
Date-Received: Thu, 16-Apr-87 11:52:52 EST
References: <16646@sun.uucp>
Organization: U of Toronto Zoology
Lines: 20
Keywords: float point expression

> ... optimizing compilers should be designed to
> improve carefully-written code by means that can not be readily expressed
> in the source language.  I would have thought that most experienced C
> programmers would agree with that proposition, but some recent postings
> suggest otherwise: that a major purpose of optimizing compilers is to clean
> up after careless coders and thereby encourage careless coding.
	  
Not quite.  The correct statement is that a major purpose of optimizing
compilers is to do machine-specific optimizations on machine-independent
code.  In C in particular, it is possible to express many optimizations
in the source code.  Unfortunately, when one does this, one often makes
the code more efficient on one machine at the cost of making it less
efficient on others.  Sometimes, in fact, one makes it more efficient on
one machine at the cost of making it unrunnable on others.  Almost always
one makes it more efficient on one machine at the cost of making it less
readable to human beings.  One legitimate role of optimizing compilers
is to remove the need for such penny-wise-pound-foolish "optimization".
-- 
"We must choose: the stars or	Henry Spencer @ U of Toronto Zoology
the dust.  Which shall it be?"	{allegra,ihnp4,decvax,pyramid}!utzoo!henry